Brief Description of the Prior Art
An electroencephalograph is an instrument for recording the electric activity of the brain by means of electrodes attached to, or in electrical contact with, the surface of the scalp. The instrument is used in the diagnosis of epilepsy, trauma, tumors and the degenerations and malfunctions of the brain.
A number of types of electrode caps for use in encephalographic analyses have been heretofore proposed, and many are described in United States patents. These devices have also been the subject of many articles and papers appearing in the technical literature.
As described in the E.E.G. Handbook, Second Edition, authored by Alice Craib and Margaret Perry, copyright Beckman Instruments, Inc., 1973 and 1975, the authors describe some of the problems which have characterized efforts to optimize encephalographic electrode caps. Craib et al indicate that it has been difficult to provide a cap construction which is economically feasible, yet electrogpraphically reliable. The authors describe a cap developed for use by astronauts in space exploration. A disadvantage which has characterized these caps is indicated to be the fact that the electrode positions are fixed, and are not individually adjustable for the requirements peculiar to each individual electrographic analysis and patient. Moreover, the construction is such that it is not possible to replace individual electrodes if they become defective or damaged. Rather, the entire cap must replaced.
Another art-recognized desideratum in electrode cap design is the elimination of artifacts due to positioning of the electrodes too close to the skull, or resulting from movement of the head of the patient relative to the cap and the electrodes carried thereby. It is also of paramount importance to avoid electrical shock and the employment of combustible or chemically reactive interface pastes is to be avoided.
In some of the proposed electrode caps heretofore patented and/or in use, two part electrode elements are provided which snap together to provide electrode exposure in the inner side of the cap, and an electrical connection to a detachable lead on the outer side of the cap. One such construction is described and illustrated in Sams U.S. Pat. No. 4,323,076.
Many of the caps previously proposed are made of an elastic material, or of a group of elastic straps which collectively hold and position the electrodes adjacent the scalp of the patient. When placed in position on the head of the patient such head gear is alleged to reduce the possibility of shifting or movement of the electrodes, or loss of electrical contact with the patient during taking of the electroencephalogram.
Generally, placement of the electrodes relative to the skull follows a standardized and systematic arrangement which is conventional in the art. For the most part, the types of electrode caps which have been proposed, depend upon rather precise measurement of electrode position on the fabric of the cap during its construction, and proper positioning of the electrodes is thus dependent upon the accuracy of this original measurement and construction.
Various methods have been proposed for retaining the cap on the patient's head during the taking of the electroencephalogram. Chin straps which pass from opposite sides of the cap under the chip of the patient are sometimes utilized. In other arrangements, such as that shown and decribed in U.S. Pat. No. 4,085,739, a chest harness is utilized so that, should the patient's chin move during the analysis, spurious signals are not developed as a result of such movement, and the cap is maintained in a relatively stable and unshifting location on the patient's head.
In an article entitled "Electrode Systems for Recording the E.E.G. in Active Subjects," Hanley, Hahn and Adey, describe an expandable Lycra electride helmet which carries grommets sewn into the helmet at spaced locations. Internal sponge electrodes snap into these grommets, and an electrolyte gel is used to soak the sponge electrode tips for establishing a good electrical path to the scalp. The Hanley et al article appears in BioMedical Electrode Technology, Academic Press, 1974.
In an article "A Method for Locating Scalp Electrodes and Spherical Coordinates," Ary, Darcey and Fender, IEEE Transactions of BioMedical Engineering, Vol. Eme-28, No. 12, December, 1981, an electrode cap is described in which the electrodes are cylindrical elements which are plugged into rubber bumper grommets located at spaced locations around the cap. These electrodes are fixed in their positions once the cap is assembled, and cannot be spaced at any selected spacing other than those dictated by the location of the rubber bumper grommets into which they are received. An elastic strap is used to hold the helmet or cap on the head of the patient.
Rolston U.S. Pat. No. 3,490,439, describes an electrode cap made up of a plurality of interconnected straps which carry a series of spaced electrodes. These electrodes are detachable from the straps, so that should one of the electrodes become defective, it can be individually replaced.
In U.S. Pat. No. 3,669,110 to Lowe et al, a disposable sponge electrode is described which can be suitably mounted in an electrode cap, and which incorporates a paste-like electrolyte material in the sponge to establish good ohmic contact with the scalp of the patient.
In U.S. Pat. No. 3,998,213, a self-adjustable holder for automatically positioning encephalographic electrodes is disclosed. The holder consists of a group of straps which are arrayed to form a head-shaped cap which is elastically expandable, and thus is self-adjustable to snugly fit the patient's head. A plurality of electrode positioning elements are located on the straps at various points, and each is adapted to hold an electrode in contact with the head at a precise position. The electrode positioning elements are made of a rigid material, and have an opening therethrough for the insertion of an associated electrode. The electrodes are made of a conductive sponge material of a type conventionally employed, and are impregnated with a conductive cream or gel of electrolyte material.
In Ricketts U.S. Pat. No. 4,026,278, a belt is provided for surrounding the body for use in electrocardiogram procedures. On the inner surface of this belt, Velcro loop fabric is attached. A series of electrodes are each provided on one side with Velcro hook fabric, and this permits the electrodes to be removably secured to the inner side of the belt at any selected locations therealong. In a different embodiment of the invention, the electrodes may be snap-engaged with cooperating snap elements carried on the belt at various locations therealong. The Velcro construction of the inner side of the belt enables the electrodes, when they carry Velcro hook fabric, to be quickly removed from the belt simply by pulling them off, and to then be repositioned by pressing them back onto the belt at the newly desired locations. The number of electrodes employed can be varied.
A generally similar attachment system is described U.S. Pat. No. 4,072,145 to Silva. Here a head band assembly of electrodes for sensing signals of brain wave frequency is disclosed. The assembly includes a head band and is constructed of self-adherent Velcro material. The electrode subassemblies include superimposed or sandwiched Velcro pads with the innermost pad (closest to the scalp) being silver plated to afford conductivity. The Velcro outer pad of each electrode subassembly can be adhered at any selected location along the band, which is placed around the patent's head. The several electrode assemblies can thus be shifted along the band as desired to adjust their location relative to the cranium.
In U.S. Pat. No. 4,033,334, a replaceable electrode is disclosed which is constructed to include a plastic housing containing a sponge body which is filled with conductive electrolyte gel. The base of the housing is formed of a conductive plastic material and has at its center, a snap-engaging element. This element cooperates with a co-acting snap element located on a washable electrode cap. The electrode may be easily replaced at any time or following each use. As in many other types of prior art electrode caps, the correct positioning of the electrodes against the scalp is accomplished by precision fitting of the cap.
The described devices for positioning various types of electrodes in electrical contact with the scalp of a person undergoing an electroencephalographic analysis still lack flexibility and universality in the capability they afford for selectively and precisely adjusting the postion of numerous electrodes relative to the cranium of the patient. Moreover, the time required to achieve the necessary electrode positioning preparatory to commencing to record the brain wave signals is still unacceptably lengthy.